Notes: Wed 25 Sept
Reminders about ozone
- Ozone depletion is an anthropogenic effect, meaning it is man-made.
The compounds responsible for enhancing ozone depletion are chloroflourocarbons, or CFC's.
CFC's were designed to be safe and inert (non-reactive) on the ground.
Their non-reactiveness is what allows them to make it up to the stratosphere.
- Ozone depletion occurs everywhere. It is most intense at the South Pole because the vortex of cold wind in wintertime there helps to free up chlorine.
In spring, this chlorine interacts with the sun to make the chlorine ion, which attacks ozone.
However, the vortex also starts to dissipate in the spring, which stops chlorine production. The hole is closed up when the reactive chlorine is put back in
safe reservoirs and fresh air comes from low latitudes.
- CFC's do not concentrate at the South Pole. That is just where ozone depletion is worst.
The highest levels of chlorine in the atmosphere are over the northern hemisphere, close to industry. However, the atmospheric conditions are not conducive to such strong ozone depletion as at the South Pole. Notice that the North Pole
also does not have strong depletion because it does not have the cold winter vortex.
- Stratospheric circulation is important. We have seen that it disseminates chlorine around the globe and replenishes ozone.
Why is ozone depletion still so controversial?
- Data indicate the amount of depletion is increasing. Is there a threshold
past which the ozone layer will not be able to repair itself as usual? We don't know.
- Science issues are poorly communicated. The people with power over research
in this field often do not have their facts straight and base their arguments on questionable sources.
- The complex system of stratospheric chemistry actually is not entirely
understood. This makes it hard to make any definitive statements, which is what
the public demands.
- The magnitude of harmful effects is unknown because the data are incomplete.
(we have not correlated ozone depletion with increased UV radiation.)
- Eliminating CFC's is a global problem, practically speaking.
- it would hurt the CFC industry
- how does one legislate it?
- finding a replacement material takes time and money
The Celsius and Fahrenheit scales: F=9/5*C + 32. Water boils at 212 deg.F and 100 deg. C. Water freezes at 32 deg. F and 0 deg. C.
overhead of temperatures in Ann Arbor in September: as the month
goes by, the following all decrease: average high temperature, average low temperature, maximum (highest) temperature, and minimum (lowest) temperature.
Controls on temperatureamount of insolation received, which is strongly latitude dependent.
altitude: there are less gas molecules higher up, so there's less ability to absorb heat. There are greater ranges in temperature at higher altitudes.
cloud cover: the most variable of the factors. About 1/2 of the Earth is
covered every day by clouds. Even though clouds block out the sun, they also
act as a blanket so that it's harder for heat from the Earth to escape.
In this fashion, clouds are an insulator which moderates temperatures; it won't get as hot but it won't get as cold, either.
Differences between land (continental) and ocean (maritime) climatesocean temp's are more moderate
land temp's are extreme
- evaporation: evaporation takes up heat (latent heat). More evaporation takes place over oceans, so more heat is taken up over oceans.
- transmissibility: light can go down into the top layer of the ocean (the "photic layer"). This spreads out the incoming radiation whereas on land, the surface gets all of the incoming energy and so heats up more rapidly.
- specific heat: it's the amount of energy needed to raise an amount of something by 1 degree C. Water has high specific heat and continents do not.
The general idea is that it takes a lot of energy to heat up
water and not so much energy to heat up land. The reverse is true, too. Land
cools easily and water does not. Since land heats up and cools so easily, the temperatures will change more frequently and with greater magnitude than over oceans. So temperatures are more moderate over oceans than continents.
- movement: advection/convection/mixing of water spreads heat out over a greater volume, so ocean climes are more mild and uniform.
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